The present invention relates to rotary pumps and motors, and more particularly but not exclusively to motors employed in well formations to drive the cutting head of a drill string.
Disclosed in U.S. Pat. No. 4,187,064 is a rotary motor/pump which includes a central shaft surrounded by an outer housing. The shaft has an outer peripheral surface having at least one lobe while the other housing has a generally cylindrical inner surface in sliding contact or located adjacent the lobe. The outer housing is also provided with a plurality of radially movable gates. The gates co-operate with the lobe to provide variable volume working chambers which receive a working fluid under pressure when the device is acting as a motor or which exhausts a fluid under pressure when the device is acting as a pump or compressor. Relative rotation occurs between the shaft and the outer housing to vary the volume of the chambers.
Earlier rotary machines included steam engines such as those described in U.S. Pat. Nos. 349,888, 389,328, 664,486, 1,900,784, 371,949, 398,988, 500,988, 590,581, 355,479, 604,709 and 866,677. Although a variety of rotary motors are described their configuration is such that they are unemployable in a drill string of a well formation.
Fluid pumps and/or fluid motors are described in U.S. Pat. Nos. 2,232,951, 3,426,694, 445,318, 3,134,335 and 3,241,456. Again although a variety of rotary machines are described they are unemployable in a drill string.
An internal combustion engine is known having a rotor with an outer housing, with the rotor joined to the housing by means of radially reciprocated vanes. In one embodiment the vanes have rollers which engage a cam groove in the rotor. Again this device is unemployable in a drill string.
There is disclosed herein a rotary machine through which a working fluid passes, said machine comprising:
a central shaft means having a radially outer peripheral surface provided with at least one lobe having a maximum radius relative to the longitudinal axis of the shaft means;
an outer housing having an inner cylindrical surface surrounding the shaft means, the inner surface having a radius approximately equal to said maximum radius;
bearing means extending between the housing and shaft to provide for relative rotation therebetween;
a plurality of gates movably mounted in the housing for movement between a retracted position at least substantially located in said housing and an extended position protruding from said housing;
said gates, shaft and housing co-operating to define at least two variable volume working chambers, the volumes of which change with relative rotation between the shaft means and housing about said axis;
first duct means extending through said shaft and communicating with the chambers at a position adjacent to said lobe on a first angular side thereof;
second duct means extending through said shaft and communicating with said chambers adjacent said lobe on the other angular side thereof to the first duct means; and
wherein relative rotation between said shaft means and housing provides for movement of said working fluid through said chambers via said first and second ducts.
In the rotary machine above, preferably the shaft means includes longitudinally extending fluid inlet and outlet passages forming part of said first and second duct means, said inlet passage extending to a plurality of inlet passage portions, and said outlet passage extending from a plurality of outlet passage portions, with the inlet passage portions and outlet passage portions being longitudinally co-extensive and with said inlet passage extending from a first end of said shaft and said outlet passage extending from an opposite end of said shaft to said first end.
In the above rotary machine, preferably said rotary machine is a motor, with said shaft means consisting of a shaft and a stator mounted thereon, said stator providing each lobe, said shaft having an outer diameter and an inner diameter according to the following formula:
Dm less than D{1xe2x88x92(2Pxc3x9710xe2x88x927)/(ND3)}0.25
where
P=power rating of the machine (Watts)
N=speed rating of the machine (rev/min)
D=shaft outside diameter (m)
Dm=shaft inside diameter
In the above rotary machine, preferably said outer housing has a wall thickness, and each lobe has a radial lobe height, with the wall thickness being such that:
Wt greater than 1.2L
where
Wt=wall thickness of outer housing
L=lift of stator (height of lobes)
where Wt is the wall thickness and L is the radial height of each lobe.
In the above rotary machine, preferably each shaft means includes a stator portion providing each lobe and having a radially outer surface, and each gate has a radially inner surface adjacent the radially outer surface of the stator, and a gate radial outer surface, with each gate further including a passage extending between the gate radially inner and radially outer surfaces.
In the above rotary machine, preferably the shaft means includes a stator providing each lobe, and the gates are of a xe2x80x9cyokexe2x80x9d configuration so as to provide a base from which there radially inwardly extends a pair of generally parallel transversely spaced coextensive legs, and the stator includes cam means operatively associated with the legs to cause radial movement of the gates in coordination with movement of the gate relative to the lobes.